How do you texture with a photo taken from an angle without distorting it based on the polygons?
I am maybe misunderstanding what you are trying to do but will ask anyways.If all you are trying to do is map the 2D image to the 3D box shape why are you using any subdivisions at all ?
Surely the simplest approach is to select the 3 appropriate faces of the simple cuboid and U to open the UV Mapping menu and choose the Unwrap option, then reposition the 7 vertices in the UV space as accurately as you can over the image.